A vast dust storm larger than the entire North American continent is currently raging on Mars—and it has forced NASA to suspend the scientific operations of its Opportunity rover.

The storm—which covers an area of more than 7 million square miles—was first detected on Friday by the space agency’s Mars Reconnaissance Orbiter. NASA officials quickly notified the rover’s operating team so they could begin contingency planning.

“Full dust storms like this one are not surprising, but are infrequent,” according to a NASA statement. “They can crop up suddenly but last weeks, even months. During southern summer, sunlight warms dust particles, lifting them higher into the atmosphere and creating more wind. That wind kicks up yet more dust, creating a feedback loop that NASA scientists still seek to understand.”

The dust has blotted out the Sun in many regions, including Opportunity’s current location at Perseverance Valley. This is a problem because the rover uses solar panels to provide its power and recharge its batteries. The rover has now been shifted to minimal operations in a bid to conserve energy, while still providing just enough electricity to run its heaters.

“Engineers will monitor the rover's power levels closely in the week to come,” NASA officials said. “The rover needs to balance low levels of charge in its battery with sub-freezing temperatures. Its heaters are vitally important to keeping it alive, but also draw more power from the battery.”

There is a chance that the extreme cold could put Opportunity out of action for good if the storm persists for too long. Cold is thought to have resulted in the loss of Spirit—Opportunity’s twin—in 2010, which became stuck in the Martian sand.

This global map of Mars shows a growing dust storm as of June 6, 2018. The map was produced by the Mars Color Imager (MARCI) camera on NASA's Mars Reconnaissance Orbiter spacecraft. The blue dot indicates the approximate location of Opportunity. NASA/JPL-Caltech/MSSS

But Opportunity has survived adverse weather events in the past. In 2007 a much larger dust storm covered the entire Martian surface, forcing the rover to switch to minimal operations for a whole two weeks.

Opportunity (and Spirit) landed on the Red Planet in January 2004. The rover was only designed to last 90 days but has vastly exceeded expectation, and is currently in its 14th year on the Martian surface.